linux-kernel - [PATCH RESEND 1/2] prctl: Generalize PR_SET

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Date: Mon, 26 Feb 2024 17:35:41 -0800
From: Zev Weiss <zev@...ilderbeest.net>
To: Russell King <linux@...linux.org.uk>,
	linux-parisc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Helge Deller <deller@....de>,
	Florent Revest <revest@...omium.org>
Cc: Zev Weiss <zev@...ilderbeest.net>,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	"Borislav Petkov (AMD)" <bp@...en8.de>,
	Yin Fengwei <fengwei.yin@...el.com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Yang Shi <yang@...amperecomputing.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	David Hildenbrand <david@...hat.com>,
	Stefan Roesch <shr@...kernel.io>,
	Josh Triplett <josh@...htriplett.org>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	linux-kernel@...r.kernel.org,
	openbmc@...ts.ozlabs.org,
	Sam James <sam@...too.org>,
	stable@...r.kernel.org
Subject: [PATCH RESEND 1/2] prctl: Generalize PR_SET_MDWE support check to be per-arch

There exist systems other than PARISC where MDWE may not be feasible
to support; rather than cluttering up the generic code with additional
arch-specific logic let's add a generic function for checking MDWE
support and allow each arch to override it as needed.

Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
Cc: <stable@...r.kernel.org> # v6.3+
---
 arch/parisc/include/asm/mman.h | 14 ++++++++++++++
 include/linux/mman.h           |  8 ++++++++
 kernel/sys.c                   |  7 +++++--
 3 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 arch/parisc/include/asm/mman.h

diff --git a/arch/parisc/include/asm/mman.h b/arch/parisc/include/asm/mman.h
new file mode 100644
index 000000000000..47c5a1991d10
--- /dev/null
+++ b/arch/parisc/include/asm/mman.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <uapi/asm/mman.h>
+
+/* PARISC cannot allow mdwe as it needs writable stacks */
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+	return false;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+
+#endif /* __ASM_MMAN_H__ */
diff --git a/include/linux/mman.h b/include/linux/mman.h
index dc7048824be8..bcb201ab7a41 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -162,6 +162,14 @@ calc_vm_flag_bits(unsigned long flags)
 
 unsigned long vm_commit_limit(void);
 
+#ifndef arch_memory_deny_write_exec_supported
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+	return true;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+#endif
+
 /*
  * Denies creating a writable executable mapping or gaining executable permissions.
  *
diff --git a/kernel/sys.c b/kernel/sys.c
index f8e543f1e38a..8bb106a56b3a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2408,8 +2408,11 @@ static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
 	if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
 		return -EINVAL;
 
-	/* PARISC cannot allow mdwe as it needs writable stacks */
-	if (IS_ENABLED(CONFIG_PARISC))
+	/*
+	 * EOPNOTSUPP might be more appropriate here in principle, but
+	 * existing userspace depends on EINVAL specifically.
+	 */
+	if (!arch_memory_deny_write_exec_supported())
 		return -EINVAL;
 
 	current_bits = get_current_mdwe();
-- 
2.43.2